get_mconstants (3) - Linux Manuals

get_mconstants: retrieve a list of constant values from a dirfile


get_mconstants --- retrieve a list of constant values from a dirfile


#include <getdata.h>
const void *get_mconstants(DIRFILE *dirfile, gd_type_t return_type, const char *parent);


The get_mconstants() function queries a dirfile(5) database specified by dirfile and returns a read-only list of values of the all CONST type metafields for the supplied parent field after type conversion to the data type specified by return_type.

The dirfile argument must point to a valid DIRFILE object previously created by a call to dirfile_open(3).

The array returned will be de-allocated by a call to dirfile_close(3) and should not be de-allocated by the caller. The list returned should not be assumed to be in any particular order, although it is guaranteed to be in the same order as the list of CONST fields returned by get_mfield_list_by_type(3). The array is unterminated. The number of values in the array can be obtained from a call to get_nmfields_by_type(3).

The caller may not modify any values in the array, or the array itself. Doing so may cause database corruption. The pointer returned is guaranteed to be valid until get_mconstants() is called again with the same arguments, or until the array is deallocated by a call to dirfile_close(3).

A corresponding list of names for these fields may be obtained by calling get_mfield_list_by_type(3).


Upon successful completion, get_mconstants() returns a pointer to an array of values containing the values of all the CONST metafields for the supplied parent field. If the parent field has no constant metafields, NULL is returned. On error it returns NULL and sets the dirfile error to a non-zero error value. Possible error values are:
The library was unable to allocate memory.
The supplied parent field code was not found, or referred to a metafield itself.
The supplied dirfile was invalid.
The return_type specified was invalid. The dirfile error may be retrieved by calling get_error(3). A descriptive error string for the last error encountered can be obtained from a call to get_error_string(3).